12* MORPHOLOGY AND EVOLUTION pyriform. It is bounded above by the lower border of the conjoined nasal bones, and below and laterally by the premaxilias, which extend upwards to meet the nasal. The anterior nasal spine is very frequently, but not always, absent. And small tubercles may be found in this region; these, however, must not be regarded as nasal spines. At the sides of the lower part of the. narial aperture the sockets for the upper canine teeth form pronounced swellings. In young skulls the maxillo-premaxillary sutures are evident running parallel to the nasal margin. The premaxillaB are about the same size as those in the Chimpanzee, but their anterior surfaces are not so undulated by the sockets of the incisor teeth in the Gorilla. The malar bones are convex outwardly. Their vertical extent is greater than the transverse, whereas the reverse is the case in the Chimpanzee. Horma Lateralis,—When the skull is viewed from the side the great size of the jaws compared with the cranium is at once evident, and the size of the cranium appears dwarfed by the temporal, sagittal and lambdoid cristae. The size of these cristae depends on age and sex, and Eothschild (485) shows that the characters are of value for distinguishing between sub-species (see page 101), In the very young skull the temporal ridges run backwards without meeting. As age advances, coexistent with the enlargement of the jaws and temporal muscles, the ridges approach and meet on the sagittal line. In the female they unite to form a small sagittal crest or a series of ridges and furrows. They form a marked crest in the male which varies from 20-45 mm. in height (Duckworth); but a height of 40-45 mm. is not very common.